SAT Subject Biology Practice Question 97: Answer and Explanation

Next steps

Question: 97

7. Edward's syndrome is the result of an additional 18th chromosome present in a fertilized embryo. Which of the following events could lead to the presence of this additional chromosome in a zygote?

A. Crossing over in meiosis I
B. Nondisjunction in meiosis II
C. A deletion during meiosis II
D. A deletion during meiosis I
E. Replication error in meiosis II

Correct Answer: B


Nondisjunction occurs when two homologous chromosomes or chromatids fail to segregate; if this were to occur in meiosis I or II, the resulting zygote could have three copies of a chromosome.

Previous       Next